Although Pip is a young boy when the story starts, the story is narrated by his older self. Pip is not born a gentleman, but he becomes one when he is given his “great expectations.”
Pip is most certainly not a gentleman as the story opens. He is a blacksmith’s nephew, and an orphan raised by his sister. However, the story he is telling is of how he came to be a gentleman. He is a gentleman when he is telling the story.
“Has she been gone long, Joe?” I always treated him as a larger species of child, and as no more than my equal. (ch 1, p. 8)
You can tell that the voice that is explaining this is an older, mature, educated voice. This contrasts with the child he is remembering.
There are several glimpses of the older Pip in the narration. It is not from a child’s point of view, it is from the point of view of an adult remembering. He explains that the story with the convict is his “first most vivid and broad impression of the identity of things” (ch 1, p. 4). The actual dialogue when Pip says something is usually pretty unsophisticated at this point, but his thoughts are developed. This is because they are the thoughts of an adult and the words of a child.